Evaluating queries with outer joins by categorizing and...

Details Evaluating queries with outer joins by categorizing and... Evaluating queries with outer joins by categorizing and...

2005-02-01

2005-02-01

Metjahic, Safet (Department: 2171)

Data processing: database and file management or data structures

Database design

Data structure types

C707S793000, C707S793000

Reexamination Certificate

active

06850927

ABSTRACT:
Aspects of the invention provide methods for rewriting and computing database queries that include outer join conditions, and for determining columns that satisfy a criteria. According to one aspect, a component relation key is assigned to each unique column in a first table and an aggregate relation key is generated for each record in a second table, wherein the aggregate relation key is based on one or more of the component relation keys corresponding to columns with non-null values from the second table. Distinct aggregate relation keys are determined, and an original query with an outer join is rewritten into at least a number of sub-queries equal to the number of distinct aggregate keys, wherein each sub-query includes a join condition based on each column represented by the respective distinct aggregate keys. Significantly, the combination of sub-queries is logically equivalent to the original query, but does not include outer join conditions. Therefore, a more efficient query is provided.

REFERENCES:
patent: 6385603 (2002-05-01), Chen et al.
patent: 20030088558 (2003-05-01), Zaharioudakis et al.
patent: 20030120682 (2003-06-01), Bestgen et al.
Colin L. McMaster, “An Analysis of Algorithms for the Dutch National Flag Problem”, Oct. 1978, vol. 21 No. 10, pag 842-846.

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